High performance vacuum annealed <i>β</i>-(Al_xGa_1−x)₂O₃/Ga₂O₃ HFET with f_T/f_MAX of 32/65 GHz

Abstract This letter reports high performance β - (Al x Ga 1−x ) 2 O 3 /Ga 2 O 3 Heterostructure FET (HFET) with an improved regrowth process and successful Al 2 O 3 passivation. Highly scaled I shaped gates (100–200 nm L G ) have been fabricated with degenerately doped (N++) source/drain contact regrown by ozone molecular beam epitaxy (MBE). Aiming to address the limitations observed in previously reported devices, this work incorporates a low-power BCl 3 /Ar and SF 6 /Ar plasma etching process to remove the AlGaO barrier layer and Ga 2 O 3 layer respectively before regrowth. Additionally, the surface was cleaned, and vacuum annealing was carried out before MBE regrowth to reduce any interface resistance between highly doped regrowth N++ and 2DEG layer. These meticulously designed fabrication steps enabled us to achieve the high DC current 0.5 A mm −1 at 5 V drain bias with 6.1 Ω.mm on resistance (R ON ) at V GS = 3 V, peak transconductance (g m ) of 110 mS mm −1 at room temperature (V DS = 15 V) and around 0.8 A mm −1 (V DS = 5 V) peak I ON at low temperature (100 K). The current gain cut-off frequency (f T ) of 32 GHz and peak power gain cut-off frequency (f MAX ) of 65 GHz were extracted from radiofrequency (RF) measurements. The reported f MAX is one of the highest for Ga 2 O 3 based RF devices to the best of the authors’ knowledge. The f T .L G product was estimated to be 6.1 GHz- μ m for 191 nm L G and 32 GHz f T , which is one of the highest reported among Ga 2 O 3 devices. After passivating the device with thicker Al 2 O 3 , the device shows no current collapse demonstrating first time successful traps passivation with Al 2 O 3 for β -Ga 2 O 3 devices.